Fungi known as endophytes grow inside certain grass species, but do not harm them.

Grasses that contain endophytes are more resistant to certain insect pests because these fungi produce alkaloids that act either as a direct toxin to some pest species or as a feeding deterrent to others.

Although endophytes may deter chinch bugs, cutworms and sod webworms, they have no significant effect on root-feeding insects such as white grubs.

Soil contains millions of bacteria and fungi that can degrade pesticides. Although this is beneficial for the environment, it can cause pesticide treatments to fail.